Circuit employing reflex klystron with protective diode



Oct. 27, 1959 N. J. ALSTAD ETAL CIRCUIT EMPLOYING REFLEX KLYSTRON WITH PROTECTIVE DIODE Filed June 28, 1957 i Nl/NTO/P F A/O/P/MA/V JAASTAD aoeao/v 5 Chm/0450 2,910,612 I t CIRCUIT EMPLOYINGREFLEX K LYST RON WITH rnorncrrvnmonn Norman J. Alstad,- Wayland, and Gordon E. Chandler,

Winchester, Mass,.assignorsttoRaytheonCompany, a

This invention relates to circuits employing klystrons of the reflex type supplied with a built-in protective diode. i e

One of themosttroublesome problems in the operation of a reflex klystron oscillator, particularly when voltagemodulated, is the condition of run-away reflector current. This may occur when primary electrons from the cathode are allowed to impinge on the surface of the reflector. These impinging electrons have a tendency to free secondary electrons from the surface of the reflector, which are then attracted to the positively charged upper grid. A current is thereby set up through the resonator and reflector power, supply circuitry. As is well known to those skilled in the art, it is common practice to employ a reflector circuit having a high series impedance therein (e.g., a resistor of large value) to provide coupling to an external circuit such as the output of a modulator. Also, the reflector voltage supply is often potentiometric in nature, thus introducing additional series impedance in the reflector supply circuit. As a result, when the aforementioned secondary emission current flows in the reflector circuit, the voltage drop appearing across the large series impedance thereof tends to bias the reflector increasingly less negative with respect to the cathode. Accordingly, an increasing percentage of the primary electrons from the gun strike the reflector and increase the positive bias of the reflector, causing further electrons to be emitted from the reflector, and so on, until there is a run-away condition. This current reaches equilibrium when the secondary emission capabilities of the reflector reach saturation. But by this time, physical damage has been done to the reflector tube parts within the envelope. As is evident, where a low-impedance reflector circuit is employed (as is the case in certain applications, with the modulator or other external circuit being transformer-coupled rather than resistor-coupled to the reflector circuit), the aforementioned run-away will generally not occur.

Under normal recommended oscillating conditions of a reflex klystron, of course, no primary electrons are allowed to strike the surface of the reflector by virtue of the negative potential maintained on the reflector with respect to the cathode. However, any surge of electrons allowed to strike the reflector may set oh? the run-away condition where the reflector circuit impedance is large. Such surges can be prevented from causing run-away by applying the reflector potential before the resonator potential is switched on. This can be done in some applications by using a time delay on the resonator potential supply in the form of a time switch or slow heating of the rectifiers in the resonator power supply circuit. However, the aging of the rectifier tubes in the power supplies may make these measures inadequate. These measures may also prove inadequate where the reflector voltage is modulated. Thus it has been found better to connect a diode between the re- A United States Patent cc 2,910,612 Patented Oct. 27, 1959 flector and cathode across the reflector'power supply and the impedance in series with it to provide a low impedance path for reflector current around the reflector circuit impedance, preventing any appreciable drop in the reflectorvoltage with respect to the resonator. However, such a diode-requires aheater supply an'doccupies space. Space andweight of equipment must be reduced to a minimum in certain-applications, such as inmissile's and other aeronautic vehicles.

Bythepresent invention this diodeis made integral with the klystron by adding anelectron-emissive deposit on the'side of the cathode sleeve in addition to the emissive depositon the end of thecathode assembly. In this position, the auxiliary emitter deposit" is also heated to electron-emitting temperature andno auxiliary heat source is required. A simple rod electrode may be brought through the envelope by any convenient method so long as it is insulated fromthe other electrodes and formsa vacuunntight seal in passing through the envelope. The electrode constituting the anode of this diode is connected to the reflector ofthe tube either within or without the envelope.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings wherein:

Fig. 1 is a schematic diagram of a circuit embodying the invention;

Fig. 2 is a side view, partly in section, of a klystron incorporating the diode of the invention; and

Fig. 3 is a detail of the tube of Fig. 2 showing the diode of the invention on an enlarged scale.

In Fig. 1, the reference numeral 10 designates schematically the reflector of a klystron-type electron tube having a pair of grids 11 and 12 associated with a cavity resonator 13 and a cathode assembly 14. The cathode assembly 14 comprises a cathode sleeve 15 with a coating 16 of electron-emissive material on its closed end and a second deposit 17 of such material on its side. The cathode also includes a heater element 13 enclosed within the sleeve 15 and supplied with electrical power from a source of potential 20. An electrode 21' of conductive material is mounted with its end 22 adjacent the deposit 17 of emissive material and the other end connected to the reflector 10.. The reflector is also connected to the cathode 15 through a normally large impedance 23 and a source 24 of negative potential. The resonator 13 is connected to the cathode 16 through a source 25 of potential.

The construction of the klystron-type tube incorporating the invention is shown in more detail in Figs. 2 and 3 in which the reference numeral 30 designates the glass envelope supporting the grids 31 and 32 and the associated cavity resonator 33, which, in turn, support the reflector sleeve 34 and the reflector 35. The electron gun assembly 36 is also mounted within the envelope. It comprises the sleeve and control electrode 37 and the cathode assembly 38 with the emissive coating 40 on the end and an emissive deposit 41 on the side facing the end of the electrode 42 carried through the sleeve 37 in an insulated bushing 43 and through the envelope in a glass-to-metal seal 44 as best seen in Fig. 3.

In operation, the electrons from the gun 36 heat the reflector 35 and cause it to emit secondary electrons. These electrons flowing through the large impedance 23 develop a voltage drop of a polarity opposing the voltage of the source 24 and the reflector becomes positive with the respect to the cathode. This causes the diode formed of the emissive deposit 17 (in Fig. 1) and the electrode 21 to conduct providing a low impedance path shunting the impedance 23 and source 24. This diverts the secondary electron current from the impedance 23 along the path indicated by the reflector from going further positive and thu s prevents V the run-away effect.

arrows 46 and prevents the It will be seen that this is accomplished with only a minor change in the tube structure and the circuit, t hus efiecting a considerable saving in vbulk and weight, due tothe elimination of a separate diode and its filament supply.

. This completes the description of the embodiment of the invention illustrated herein. However, many modifications and advantages thereof will be apparent to persons skilled in 'the art without departing from the spirit and scope of this invention. Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein except as defined by the appended claim.

What is claimed is:

n An electrical circuit comprising a reflex klystron having a. reflector electrode, a resonator grid assembly, a pair of directly-connected cathodes, and an anode directly connected to said reflector electrode, a first of said cathodes being in substantial alignment with said resonator assembly and said reflector electrode to form a reflex klystron structure, the second of said cathodes being mounted adjacent said anode to form an auxiliary References Cited in the file of this patent UNITED STATES PATENTS 1,426,826 Egerton Aug. 22, 1922 2,032,781 Mark Mar. 3,1936 2,113,005 Smith Apr. 5, 1,938 2,163,217 Schlesinger June 20, 1939 2,342,987 Bosch Feb. 29, 1944 2,511,789 Rosencrans June 13, 

